1. Field of the Invention
The present invention relates to a capacitor-mounted metal foil and a circuit board using the same, and a method for producing them.
2. Description of the Related Art
In recent years, with the demand for high performance and miniaturization of electronic equipment, there is an increasing demand for high density and high function of a semiconductor device. This results in a demand for a miniaturized high-density circuit board for mounting a semiconductor device.
Furthermore, when semiconductor devices are mounted at high density, heat and noise are generated by components. Thus, in order to mount semiconductor devices at high density, a circuit board is required that allows high-density mounting and is excellent in a thermal dissipation property and noise resistance.
As a technique of improving the thermal dissipation property of a circuit board, a heat-conductive substrate using a thermosetting resin and an inorganic filler has been proposed (see JP 10-173097 A). Furthermore, JP 11-168112 A has proposed a method for heating and pressurizing a sheet-shaped material containing a mixture of an inorganic filler and a thermosetting resin, thereby performing mounting and sealing of semiconductor devices simultaneously.
As a general method for enhancing the noise resistance of a circuit board, capacitors for removing noise are mounted on a circuit board so as to absorb high-frequency noise and ripple. However, in the case where capacitors are mounted on a circuit board, the size of the circuit board is enlarged so as to ensure a mounting area for the capacitors. Therefore, there has been an attempt in which capacitors are embedded in a circuit board.
For example, methods for forming a capacitor in a ceramic substrate have been proposed (JP 62-131411 A, JP 1-152688 A, and JP 2-305490 A). According to these methods, a ceramic substrate material and a ceramic dielectric material capable of being sintered under the same conditions as those of the substrate material are layered on one another, and both the materials are sintered simultaneously, whereby capacitors are formed in a ceramic substrate.
However, a conventional ceramic substrate with capacitors embedded therein entails a high cost. Furthermore, it takes a long period of time to produce a prototype of and to change the design of such a substrate. On the other hand, according to the method for embedding ceramic capacitors made of a sintered body in an inexpensive resin substrate, the sintered body may be broken when the substrate is layered to form a multi-layer structure.